Peptide transport has been studied extensively in E. coli and the lining of the intestine in various mammals. The importance of peptides in a variety of physiological processes warrants the extension of the above studies on peptide transport to other cell types. In this investigation the structural specificity of the peptide transport system in Saccharomyces cerevisiae will be determined. Attempts will then be made to label and isolate various components of the peptide transport system in E. coli and S. cerevisiae. The specificity of the transport system will be examined using the response of auxotrophs of yeast to various synthetic peptides and their derivatives. Growth of the auxotroph, protein biosynthesis, and the accumulation of radioactivity from radioactive peptides will all be used as criteria of transport. Isolation of transport-deficient and peptidase-deficient mutants will facilitate the above studies. Concurrently, the ability of various components, such as spheroplasts and isolated vacuoles, to concentrate and hydrolyze the peptides under investigation will be evaluated. The knowledge of the structural requirements of the transport system will enable the design of specific peptides which will be used to affinity label the component(s) of the transport system. The labeled membrane component(s) will be isolated using protein purification techniques including affinity chromatography. Characterization of the chemical and physical properties of this component(s) will provide insights into the nature of the interaction of peptides with cell membranes.